Color is the first and most important attribute of a cosmetic product that consumers see prior to their purchase of a cosmetic product. Stability of the color in cosmetic products is impacted by exposure to ultraviolet radiation from one or more artificial light sources as well as from direct sunlight and/or indirect sunlight.
Sunscreens are a recommended form of protection for skin from the damaging effect of ultraviolet radiation emitted by the sun whenever the skin is exposed. Repeated use of sunscreen is necessary for preventing or minimizing sunburn and for allowing a natural tan to develop. Improper use of sunscreens on skin leads to sunburn.
Improper use of sunscreens in cosmetic products leads to damage of the cosmetic product due to ultraviolet light that is analogous to damage of the skin. Ultraviolet light from artificial light, direct sunlight and indirect sunlight distorts color in cosmetics and renders it undesirable to consumers.
Ultraviolet, UV, radiation is defined as that portion of the electromagnetic spectrum between x rays and visible light, between 40 and 400 nm (30-3 eV). The UV spectrum is divided into vacuum UV at 40-190 nm, far UV at 190-220 nm, UVC at 220-290 nm, UVB at 290-320 nm, and UVA at 320-400 nm. The sun is a primary natural source of UV radiation. Artificial sources include black lights, mercury vapor lamps, halogen lights, high-intensity discharge lamps, fluorescent and incandescent sources. Unique hazards apply to the different sources depending upon the wavelength range of the emitted UV radiation. The UVC source of radiation is almost never observed in nature because it is absorbed completely in the atmosphere, as are far UV and vacuum UV.
UVB is typically the most destructive form of UV radiation because it has enough energy to cause photochemical damage and is not completely absorbed by the atmosphere. UVA is the most commonly encountered type of UV light. UVA exposure has an initial pigment-darkening effect that causes tanning on skin. Atmospheric ozone absorbs very little of this part of the UV spectrum. On exposure to UV A-B radiation, atoms of a color compound undergo a change by exiting their electrons to a higher energy level. This electron transition contributes to a discoloration of a cosmetic product.
There have been two basic approaches to inhibit UV light damage in a cosmetic product. One approach has used a physical blocker such as titanium oxide which acts to ward off the UV rays and create a physical blockade against incoming light. This approach is limited to specific types of cosmetics.
Another approach has used a chemical absorber which accepts the UV radiation and converts it into harmless energy such as heat. With most UV-absorbers, the benzene ring or an extended lambda-system is substituted with efficient electron-withdrawing groups. Carbonyl groups are a typical type of withdrawing group. An electron-donating group such as an amino or methoxy group is typically present in a para position to the carbonyl group. The electron-donating group often produces a so-called push/pull substituted conjugated system. This approach does not prevent adverse effects but merely limited adverse effects of UV radiation in cosmetic products.